Black rot of grapes
A fungal disease of grapes that causes brown leaf spots and turns berries into hard, shrivelled black mummies.
Also known as: Grape black rot
Symptoms and identification
Small tan to brown circular spots with a dark border and tiny black dots appear on leaves. Berries show a pale brown spot that spreads until the whole berry shrivels into a hard, black, wrinkled mummy that stays on the cluster.
Causes
The fungus survives in mummified berries on the vine and on the ground. Spores are released in spring rain and spread in warm, wet weather, with the greatest risk from bloom until berries are about half grown.
Organic treatment
Pick off and bin infected leaves and berries as soon as spotted. Copper or sulphur-based sprays used from early shoot growth may reduce the spread.
Prevention
Remove all mummified berries and prune out infected canes in winter. Train and prune vines for good airflow and sun, and keep weeds under control. Choose resistant varieties where black rot is common.
Chemical treatment (use with care)
A fungicide programme labelled for grape black rot, starting before bloom and continuing through fruit set, gives the best protection. Follow the label.